1. Field of the Invention
The present invention relates to the field of biofertilization and chemical fertilization to increase soil fertility and crop production as an adjunct to sustainable farming technology.
2. Background of the Art
There is a long history of soil fertilization. The term ‘fertilization’ includes the addition of elements or other materials to the soil to increase or maintain plant yields. Fertilizers may be organic or inorganic. Organic fertilizers are usually manures and waste materials which in addition to providing small amounts of growth elements also serve as conditioners for the soil. Commercial fertilizers are most often inorganic.
Methods of applying fertilizers vary widely and depend on such factors as crop type, stage of growth, application rates, physical and chemical properties of the fertilizer, and soil type. Two basic application methods are used, bulk spreading and precision placement. Time and labor are saved by the practice of bulk spreading, in which the fertilizer is broadcast over the entire area by using large machines which cover many acres in a short time. Precision placement, in which the fertilizer is applied in one or more bands in a definite relationship to the seed or plants, requires different equipment and time, but usually smaller amounts of fertilizer are needed to produce a given yield increase.
For some deep-rooted plants, subsoil fertilization to depths of 12-20 in. (30-50 cm) is advantageous. This is usually a separate operation from planting, and uses a modified subsoil plow followed by equipment to bed soil over the plow furrow, thereby eliminating rough soil conditions unfavorable for good seed germination. Top-dressings are usually applied by broadcasting over the soil surface for closely spaced crops such as small grains.
Nonvolatile fertilizer solutions are often pumped into the supply lines of irrigation systems to allow simultaneous fertilization and irrigation. With the exception of bulk spreaders and other broadcasters, most fertilizer application devices are built as attachments which can be mounted in conjunction with planters, cultivators, and herbicide applicators. Often the tanks, pumps, and controls used for liquid fertilizers are also used for applying other chemicals such as insecticides.
One of the major problems with these types of chemical fertilization is the fact that there are harmful effects of chemical fertilizers and their impact on the environment through nitrate contamination of ground and run-off waters. The sheer volume of fertilizers added to the soil each year is itself a major contamination problem, even if the fertilizing effects are immediately beneficial in some perspectives. It is reported that, in the United States, generally, 50% of chemical fertilizer applied to soil bypasses utilization in the soil, runs off, usually untreated, in ground water, and end up in aquifers where it represents, among other problems, a public health hazard. Alternatives to mass application chemical fertilization are therefore extremely desirable.
Biofertilizers (fertilization compositions comprising microbes) have been identified as an alternative to chemical fertilization to increase soil fertility and crop production using sustainable farming. The use of nitrogen-fixing bacteria provides plants with nitrogen compounds needed for growth and there is increasing evidence that other bacteria provide plant hormones to enhance growth.
Turf grass uses large amounts of nitrogen in the production of needed organic compounds. Most atmospheric, nitrogen is metabolically unavailable to plants and animals. The only exceptions occur when certain species of bacteria are capable of fixing atmospheric nitrogen creating organic, nitrogen-containing compounds. Bacteria with this capability are called diazotrophs. Associative nitrogen-fixing bacteria reside in close proximity to plant roots where they make a contribution of biologically available nitrogen to plants and plants to provide nutrients to the nitrogen-fixing bacteria. In addition to nitrogen fixation, Azospirillum brasilense produces plant growth hormones which have been shown to increase the number of lateral roots and root hairs (Tien, et al., 1979). These two additions could explain the increased total plant weight in the UNLV Biofertilizer treatment groups.
For the Biofertilizer, there is possibly a critical, minimum population size of diazotrophic bacteria needed for significant rates of nitrogen fixation (Wright, et al., 1981). Nitrogen fixation rates are linked to microbial growth and dependent on plant cell proliferation (National Research Council, 1994). It is known that certain strains of diazotrophs, known to be efficient fixers of nitrogen, when inoculated into the soil do not compete well against the diazotrophs already present in the soil, reducing the inoculation benefit.
U.S. Pat. No. 6,495,362 (Nautiyal) describes a biologically pure culture of bacteria that suppresses diseases caused by pathogens in chickpea crops and a culture of bacteria comprising a strain of Pseudomonas fluorescens. The patent discloses a simple live-sand or soil assay method for large scale screening of the rhizosphere-competent bacteria effective in suppressing plant pathogens. Screening for chickpea rhizosphere competitive bacteria having biological control properties were conducted at three different stages: (1) development of a screening method for large scale initial selection of bacterial isolates from chickpea rhizosphere, (2) testing of biocontrol activity under in vitro conditions, and (3) screening of antibiotic resistant mutants for rhizosphere competence in nonsterile field soil, which assay is used to disclose one Pseudomonas fluorescens NBRI 1303 (ATCC 55939) which is effective in suppressing plant pathogens, including Fusarium oxysporum f. sp. ciceri, Rhizoctonia bataticola and Phthium sp. in chickpeas, and the purified bacterial strain can be used as active agent for biocontrol compositions and can also be used for enhancement of chickpea plant growth and yield, as well as for the production of antibiotics directed towards phytopathogenic fungal diseases. The reference discloses that P. fluorescens NBRI 1303 (ATCC 55939) is an aggressive chickpea rhizosphere colonizer and can survive in the field at temperatures in the range of 0° C. to 55° C. In addition, this bacterial strain appears to produce one or more antifungal metabolites which inhibit the growth of pathogenic fungi F. oxysporum f. sp. ciceri, R. bataticola and Pythium sp. or other fungal pathogens of chickpeas since the culture supernatant exhibits growth inhibitory effects for pathogenic fungi F. oxysporum f. sp. ciceri, R. bataticola and Pythium sp. A greenhouse test and field trial of P. fluorescens demonstrated the usefulness of the strain as an inoculum for improved plant performance and therefore P. fluorescens may be used as a biocontrol agent.
Various strains of saprophytic soil bacteria are known to influence plant growth in different types of plants. For example, the inoculation of nonleguminous crops with selected strains of free-living, nitrogen-fixing species of Azotobacter and Azospirillum can cause significant increases in crop yield under field conditions. Kapulnik et al. (1981); Brown (1974). But bacteria of these genera are generally unable to compete adequately with native flora to assure multiplication. When used in seed inoculants, moreover, they are not “root colonizers,” i.e., they are incapable of transferring in large numbers from seed to roots and, consequently, cannot keep pace with developing roots. See, e.g., Reynlers & Vlassak (1982). As a consequence, impractically large amounts of inoculum are required to obtain a meaningful effect on plant growth.
Y. Kapulnik et al. inoculation of Azospirillium brasilense in Spring wheat, Biology an Fertility of Soils© Springer-Verlag 1987 Biol Fertil Soils (1987) 4:27-35 shows very limited utility for Azosprillium brasilense in treatment of Spring Wheat and especially Miriam Spring Wheat, while finding inconclusive or neutral results for other wheats.
The mechanism(s) by which soil bacteria may influence plant growth has been the subject of extensive investigation. Research into the role of microbial iron transport agents (siderophores) in the root zones of plants (the “rhizosphere”) is one mechanism by which some fluorescent pseudomonad species promote plant growth, namely, by antagonism (antibiosis, competition or exploitation) to deleterious indigenous microorganisms, resulting in their exclusion from roots.
Canadian patent No. 1,172,585 discloses the use of particular strains of naturally-occurring pseudomonads to benefit plant growth in root crops by reducing the population of other indigenous root-zone microbiota that adversely influence plant growth. Similarly, the results of one study indicated that growth-promotion in radish and potato by rhizobacteria did not occur under gnotobiotic conditions, when competition between other strains was not a factor, and hence, that rhizobacteria promote plant growth indirectly, by interaction of the rhizobacteria with native root microflora, rather than directly by microbial production of growth-promoting substances.
Another proposed mechanism for plant growth promotion by soil bacteria involves a direct stimulation of growth by bacterial elaboration of substances like nitrogen, plant hormones such as auxins and giberellins, and compounds that promote the mineralization of phosphates. But the hypothesis that elaboration of bacterial products is related to enhanced growth in plants has lacked definitive supporting data.
For example, investigations of root-elongation promotion in grasses by an auxin-overproducer mutant of Azospirillum prompted the conclusion that observed levels of the bacterially-produced auxin bore no direct relation to the root elongation. Using a petri plate bioassay for root elongation in wheat, Kapulnik et al (1985) found that seed inoculation with an A. brasilense strain resulted in root elongation in one bacterial concentration range but inhibition of root development in another, higher range. Kapulnik et al also reported that A. brasilense supernatants did not affect root length, a result arguing against a substantial role for a bacterial product in promoting root elongation. A screening of rhizosphere bacterial metabolites for in situ effects on seedling root development likewise yielded mixed results, with the observed effects ranging from complete inhibition to unaffected development; notably, no growth stimulation per se was reported.
The term “root-colonizing” is used to denote bacteria, including rhizospheric and non-rhizospheric strains, that can transfer from seed (as an inoculum component) to roots developing from the seed, and are able to maintain a stable association with the root system of the plant as it grows.
U.S. Pat. No. 6,878,179 (Porubcan) discloses fertilizer compositions for plant production comprised of decontaminated manure and Bacillus spores, preferably a humic acid derived from lignite and, optionally, one or more N-containing compounds, P-containing compounds, K-containing compounds, and combinations of two or more of these compounds. Preferred compositions are those wherein the ingredients are blended into an admixture resulting in a granular product. Other preferred compositions are those blended into an admixture resulting in a powdered product. Preferably, the ingredients are formed into hardened prills or pellets. Processes for production and use are also presented.
U.S. Pat. No. 6,228,806 (Mehta) describes a biochemical fertilizer. A broad list of microorganisms, listed by genera, is provided, including Bacillus. The need for microbial nutrients is mentioned as part of the microorganism ingredient, not the bulk organic ingredient
U.S. Pat. No. 6,312,492 (Wilson) discloses improved fertilizer effect of poultry manure by adding sulfuric acid followed by drying. Wilson teaches specifically the co-addition of cellulose containing materials.
U.S. Pat. No. 6,232,270 (Branly et al.) focuses on using Bacillus bacteria to enhance the effectiveness of chemical herbicides and lists every imaginable Bacillus ever discovered, and claims they will all benefit this purpose.
U.S. Pat. No. 5,702,701 (O'Donnell) describes the use of a unique strain of Bacillus laterosporus (BOD strain) to benefit plants.
U.S. Pat. No. 6,174,472 describes a process of forming a pellet comprised of at least sixty percent (60%) composted sewer sludge, up to forty percent (40%) cellulosic plant material and up to fifteen percent (15%) nutrient materials and chemicals for soil enhancement and plant nutrition that provides a combination of both long and short term beneficiation of soil and herbage and has no pathogenic microbes above regulatory ranges. The composted sewer sludge comprises primary sewer sludge admixed with cellulosic plant material that is thermally treated at temperatures between 140 and 180° F. during composting to destroy mesophyllic pathogenic microbes and the viability of reproducible botanicals including seeds, but leave most thermophilic soil enhancing microbes in a viable state. Additional fibrous cellulosic material and chemicals are admixed with the composted sewer sludge and the mixture pelletized in a thermal process that raises pellet temperature to between 140 to 180° F. The nutrient and chemical materials selectively comprise nitrogenous fertilizers, phosphate, potash, trace elements, herbicides, insecticides and botanical chemicals.
U.S. Pat. No. 6,025,187 describes bacterial complexes comprising at least one non-pathogenic Bacillus and at least one non-pathogenic Lactobacillus which essentially allow the conversion of inorganic nitrogen into organic nitrogen in the form of bacterial proteins, which allow the conversion of excrement into nitrogenous compounds (stable nitrogenous compounds and/or compost) and, particularly for waste having a sufficient C/N ratio (in relation to the level of solids content), into non-polluting compounds rich in fulvic acid and humic acid, by digestion and conversion of excrements, while at the same time removing the associated pathogenic germs, in particular Clostridium, Bacteroides, colibacilli, Listeria, salmonellae and staphylococci.